Reacción a "A study indicates that dinosaurs were not in decline before the meteorite impact, as some theories suggest"

This paper takes a number of lines of evidence (mostly geologic dating and a census of land vertebrates from the end of the Age of Dinosaurs in North America), and combines them to show that dinosaurs were not declining in diversity toward the end of their reign.

The fossil record is always spotty. Not all organisms or species will wind up being fossilized, and not every location on the map will have fossils forming. So there are always questions about what the real diversity of a group was in the past, and how that diversity changed with time.

This new study helps clarify an important issue: whether the Alamosaurus beds (the Naashoibito Member) of the American Southwest were the same age as the classic Hell Creek deposits of Montana, Wyoming, and the Dakotas (our classic dinosaur community from the end of the Cretaceous), or if they might be older in time. The new study combines different types of geologic data to show that the Naashoibito Member is in fact a latest Cretaceous deposit, equivalent in time to the Hell Creek. To put this another way, there were dinosaurs who were part of the Naashoibito community who would have been around to see the effects of the terminal impact.

So since we now know that the Hell Creek and the Naashoibito were equivalent in age, we see that those southwestern dinosaurs were part of the overall North American diversity at the very end. And this shows that the diversity of dinosaurs was not declining (as some researchers had thought, as far back as the late 1800s), but was still going strong.

[Regarding possible limitations] This study tells us about North America, but there is still much of the rest of the world to consider. There are some end-Cretaceous dinosaur sites in Central Europe, in India, in Siberia, and in China. There probably are some in Argentina: that is a region where this kind of detailed fine-scale geologic dating will help to resolve how South American dinosaur diversity was changing (if at all).